Filament temperature compensating device



I W. H. KOH L FILAMENT TEMPERATURE COMPENSATING DEVICE June 3, 1952 Filed Jan. 25, 1950 INVENTOR WAL r52 H. Kama ATTORNEY Patented June 3, 1952 FKLAMENT TEMPERATURE COMPENSATING DEVICE Walter Kohl", Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a

corporation of- Iowa Application January 25, 1950, Serial No. 140,507

'1? (Elaiins. i

This invention relates in general to electronic filament-tensioning devices, and in particular to the use of bi-metallic strips as compensators for expansion of filaments.

Many of the filaments used todays high powered electronic tubes have a relatively large cross-sectional area in order to facilitate the carrying of heavy currents. When such filaments are used it becomes quite a problem to maintain them in the correct spatial relationship with thev rest of the tube as changes in temperature occur. Often the temperature chang is great and the filament must go from room temperature with no current flowing therein to an emission temperature of 2000 degreescentigrade with a heavy current flowing. The increased length of filaments due to thermal expansion over this range is appreciable and it must be compensated for by some means. One example of a heavy filament is the resnatron filament which be a staple-shaped device. The ends are retained in holding rings. It is imperative that the active or electron-emitting sections of th filaments be maintained a constant distance form the center of the holding rings, and. also that the active sections remain straight.

It is an object of thi invention, therefore, to provide a filament-t'ensioning' device which will positively maintain a filament section in a fixed spatial relationshipwith a reference member.

A further object of this invention is" to provide a temperature compensating device Ofthebimetallic type which will maintain a filament section at a constant tension. v

Another object of this inventionis to provide a filament tensioning device that will maintain a plurality of filaments a constant radial distance from a central axis.

A feature of this invention is found in the provision for a bi-metallic member which is cantileverally connected to a base member adjacent an end of a filament. The filament may be stapleshaped and a s'econd-bi-metallic member may be connected adjacent the opposite end of the filament. The movement of the bi-metallic members compensate for expansion and contraction clue to temperature change.

Another feature-of thisinvention-is a provision for a bi-metallio ring which engages a plurality of strung filaments, and wherein the filament ring'contracts or expands tocompensate for the contraction or expansion of the filaments'inresponse to temperature: changes;

Another feature of this invention isfound in the provision for a bi-metallic member which extends between the legs of a stapl'e shaped filament to maintain the center section of the filament in a predetermined spatial position.

Further objects, features, and advantages of this invention will become apparent from the description and claims when read in the light of the drawings; in which Figure 1 illustrates the temperature compensating device of this invention as applied to an undeflected staple-shaped filament for maintaining the center section in a fixed spatial relationship'with a reference member;

Figure 2 illustrates the temperature compensating device of Figure 1 under heated conditions;

Figur 3 illustrates a modification of the temperature compensating device of this invention wherein a bi-metallic strip is connected adjacent a strung filament for maintaining the tension within the filament substantially constant;

Figure 4 is a further modification of this invention illustrating how a generally crescentshap'ed' bi-m'etallic member may be used for maintaining a staple-shaped filament under substantially constant tension during temperature changes;

Figure 5 is a modification of this invention i1- lust'rating'a" bi-metallic' ring which may be placed to engage a plurality of filam'ents'for maintaining-them in a' fixed spatial relationship with respect to a reference member;

Figure-6 is an enlarged perspectiv View of the holding ring of Figure 5 in contact with thefil'ament's; and

Figure '7 is an alternative structure for the holding ring.

Withreference to Figure 1, a staple-shaped filament, designated generally as it, comprises the legs I l and lz and the center portion l3: The legs H and I2 are connected to holding members it and I6 respectively. The filament staple may be made of tungsten or any other suitable material; Such filaments are of relatively heavy cross-sectional area to allow the passage of heavy current and the associated large power output requ-iredin resnatron-filament baskets. A plurality of uch filaments are spaced about the pcriphery of holding-rings with the legs: H and i2 extending radially inwardly toward the axis of the ring. A voltage is applied between the holdingrings anda heating current flows from one ring to the other ring through the filaments. Thiscurrent-causes the filaments to be heatedto anelectron-emission temperature,- thus making them-the electron source of th e tube.

In a resnatron tube an anode is placed concentrically about the filament sections and a grid is placed between the filaments and the anode. The distances between the filaments and the grid and anode, respectively, are critical because of the high frequency for which the tube is designed. It is very important, therefore, to maintain the center portion I3 of the filament staple a fixed radial distance from the axis of the holding rings, and also to maintain the filament straight. In order to accomplish this a bi-metallic strip has one end connected to the holding member I4 adjacent the leg I I of the staple filament. The bimetallic strip is positioned such that the material I8 in contact with the filament leg has a lower coefficient of thermal expansion than the other material I9 Which forms the bi-metallic strip. The other leg I2 of the filament staple may have a second bi-metallic strip 2| connected to the holding member I6, but it is not imperative that both bi-metallic strips I1 and 2I be used.

The bi-metallic strips I1 and 2!, when subjected to an increase in temperature, deflect toward the filament legs, and thus compensate for the linear thermal expansion which occurs in the center portion I3. The linear expansion of the legs II and I2 is also compensated for by the deflection of the metallic strips such that the distance from the holding members I l and I6 will not be increased. This may be accomplished by using suitable materials for the bi-metallic strips such as, for example, molybdenum and tantalum, and by obtaining the correct length of the metallic strips relative to the length of the legs I I and I2. Figure 2 illustrates the deflected condition.

It is to be observed that the bi-metallic strips provide another function other than compensation for temperature expansion, and that is to cool the ends II and I2 and thus avoid the useless waste of heating power. It is to be observed that the bi-metallic strips I! and 2| are electrically connected in parallel with the filament legs I I and I2, respectively, and thus some of the current which fiows through the center section I3 of the filament will not fiow through the end sections H and I2, but will flow through the bimetallic strips. Thus the power dissipation in the end sections is decreased while maintaining the center section at a substantially uniform temperature throughout its entire length without appreciable end cooling. It is to be noted that the bi-metallic strips are subject to a temperature change which is caused by (1) conduction from the adjacent end sections of the filaments; (2) radiation from the hot center section I3 of the filament; and (3) current flow through them.

A modification of the invention is shown in Figure 3 wherein the holding members 22 and 23 are spread further apart than in Figure 1, and a non-conducting member 24 is formed with legs 26 and 21 and the filament is stretched thereacross. The filament ends 28 and 29 are connected to the holding members 22 and 23, respectively, and bi-metallic strips 3| and 32 are connected to the holding members and to the filament ends 28 and 29. When the temperature increases, the bi-metallic strips flex inwardly toward the axis to maintain the tension in the center section 36 substantially constant. The nonconducting member 24 may be made of ceramic, which has a very low coefficient of expansion,

7 and thus, as long as the filament 25 is maintained tightly drawn across the legs of the non-conducting member, a fixed spatial relationship will be maintained between the active portion 36 and the holding members 22 and 23. Grooves 31 may be til 4 formed in the ends of the non-conducting memher to receive the filament therein, and a suitable lubricant, such as a smear of titanium, may be placed in the groove to facilitate relative movement between the filament and the non-conducting member as expansion and contraction occurs.

It is to be noted that the bi-metallic strips may be placed on either side of the filament since any deflection from a straight line will tend to tighten the active portion of the filament.

Another modification of this invention is illustrated in Figures 5 and 6 wherein a plurality of filaments 38 are strung between annular holding members 39 and M over the annular non-conducting member 42. A lei-metallic annular member 43 engages a plurality of the filaments between the holding member 39 and the non-conducting member 42. The bi-metallic member terminates in the hooks 44 and 46 which engage adjacent filaments 41 and 48 as shown in Figure 6. The ring 43 may be used for tensioning a plurality of filaments. As the temperature increases, the ring 43 reduces its radius and thus maintains the active filament sections 49 under constant tension. The filament ends 5| may be integrally formed with the ring 43 to pass therethrough as shown in Figure 7. This makes the hooks 44 and 46 unnecessary.

A further modification of the invention is illustrated in Figure 4 wherein a bi-metallic strip 52 is of a generally crescent shape and is formed with grooves 53 in either end thereof for receiving the ends II and I2 of the filament staple. Suitable insulating material such as ceramic is placed between the end of the bi-metallic strip and the filament legs to prevent passage of electric current through the bi-metallic strip. Thus in this modification, the bi-metallic strip is heated almost wholly by radiation from the active section 54.

A plurality of filaments may be tensioned by connecting a strip 52 to each filament and a ring 55 may be connected to each filament strip to maintain alignment among the bi-metallic strips.

It is seen that this invention provides temperature compensating devices for filaments. Although it has been described with respect to resnatron filaments in particular, it is not to be so limited and the broad possibilities of this invention may be applied to any other type of apparatus which it is desired to operate over a broad temperature range and to maintain constant spatial relationship with a reference member.

I claim:

1. Temperature compensating apparatus for a staple-shaped filament maintained between a pair of holding members comprising, a bi-metallic strip extending cantileverally from one of said holding members adjacent an end section of said filament, a second bi-metallic strip extending cantileverally from the other holding member adjacent the other end of said filament, and said first and second bi-metallic strips terminating adjacent the electron emitting portion of the filament.

2. A filament tensioning device for a stapleshaped filament having two end portions and an electron emitting center portion and which has either end supported in a holding member comprising, a bi-metallic strip cantileverally supported by one of said holding members and extending therefrom adjacent one of said end portions of the filament, and said bi-metallic strip terminating adjacent the electron emitting section.

3. A temperature compensating device for maintaining a center portion of a staple-shaped filament in a fixed spatial relationship with a reference member comprising, a first holding means connected to one end of said filament, a second holding means connected to the other end of said filament, a first bi-metallic strip extending cantileverally from said first holding member adjacent the one end of said filament and terminating adjacent the electron emitting portion, and a second bi-metallic strip extending cantileverally from the second holding means and in engagement with the second filament leg.

4. A temperature compensating device for a filament extending from a first holding member to a second holding member with a bifurcated bridge placed between said holding members and the filament passing there-across comprising, a first bi-metallic strip connected to the first holding member adjacent the filament end and extending along the filament to a point intermediate the bridge member and the first holding member, a second bi-metallic strip connected to the second holding member adjacent the opposite filament end and terminating intermediate the bridge member and the second holding memher.

5. A filament tensioning device, according to claim 4, wherein said bridge member is formed with filament engaging recesses in the ends of each bifurcation.

6. A filament tensioning device for a filament mounted between two holding members and passing over a bifurcated bridge member comprising, a first bimetallic member connected to one of said holding members adjacent a filament end and extending along the filament to a point adjacent said bridge member.

7. A filament tensioning device for a filament mounted between two holding members and passing over a bifurcated bridge member comprising, a first bimetallic strip connected to one of said holding members adjacent the filament end and extending along the filament to a point adjacent said bridge, and a second bimetallic strip connected to the second holding member adjacent the opposite end of the filament and extending along the filament to a point adjacent the opposite end of the filament and extending along the filament to a point adjacent said bridge member.

WALTER H. KOI-IL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,010,159 Lippincott et a1 Aug. 6, 1935 2,082,120 Ronci June 1, 1937 FOREIGN PATENTS Number Country Date 168,407 Great Britain Aug. 31, 1921 271,584 Great Britain June 2, 1927 

